Contributions Of Water Sources Research Articles

Seasonal shifts in depth-to-water uptake by young thinned and overstocked lodgepole pine (Pinus contorta) forests under drought conditions in the Okanagan Valley, British Columbia, Canada

Abstract. As drought and prolonged water stress become more prevalent in dry regions under climate change, preserving water resources becomes a focal point for maintaining forest health. Forest regeneration after forest loss or disturbance can lead to overstocked juvenile stands with high water demands and low water-use efficiency. Forest thinning is a common practice with the goal of improving tree health, carbon storage, and water use while decreasing stand demands in arid and semi-arid regions. However, little is known about the impacts of stand density on seasonal variation in depth-to-water uptake or the magnitude of the effect of growing season drought conditions on water availability. Existing reports are highly variable by climatic region, species, and thinning intensity. In this study, stable isotope ratios of deuterium (δ2H) and oxygen (δ18O) in water collected from various soil depths and from branches of lodgepole pine (Pinus contorta) under different degrees of thinning (control: 27 000 stems per hectare; moderately thinned: 4500 stems per hectare; heavily thinned: 1100 stems per hectare) over the growing season were analyzed using the MixSIAR Bayesian mixing model to calculate the relative contributions of different water sources in the Okanagan Valley in the interior of British Columbia, Canada. We found that under drought conditions the lodgepole pine trees shifted their depth-to-water uptake through the growing season (June to October) to rely more heavily on older precipitation events that percolated through the soil profile when shallow soil water became less accessible. Decreased forest density subsequent to forest thinning did not cause a significant difference in the isotopic composition of branch water but did cause changes in the timing and relative proportion of water utilized from different depths. Thinned lodgepole pine stands were able to maintain water uptake from 35 cm below the soil profile, whereas the overstocked stands relied on a larger proportion of deep soil water and groundwater towards the end of the growing season. Our results support other findings by indicating that, although lodgepole pines are drought-tolerant and have dimorphic root systems, they do not shift back from deep water sources to shallow soil water when soil water availability increases following precipitation events at the end of the growing season.

The contributions of rainfall and fog to leaf water of tree and epiphyte communities in a tropical cloud forest

IntroductionTropical cloud forest ecosystems are expected to face reduced water inputs due to climatic changes.MethodsHere, we study the ecophysiological responses of trees and epiphytes within in an Asian cloud forest to investigate the contributions of rainfall, fog, and soil to leaf water in 60 tree and 30 vascular epiphyte species. We measured multiple functional traits, and δ2H, and δ18O isotope ratios for leaf water, soil water, rainfall, and fog in the wettest (July) and driest (February) months. Using a Bayesian stable isotope mixing model, we quantified the relative contributions of soil water, fog, and rainfall to leaf water.Results and discussionRainfall contributes almost all the leaf water of the epiphytes in July, whereas fog is the major source in February. Epiphytes cannot tap xylem water from host trees, and hence depended on fog water when rainfall was low. Most of leaf water was absorbed from soil water in July, while fog was an important source for leaf water in February despite the soil moisture content value was high. In February, lower temperatures, along with reduced photosynthesis and transpiration rates, likely contributed to decreased soil water uptake, while maintaining higher soil moisture levels despite the limited rainfall. These contrasting contributions of different water sources to leaf water under low and high rainfall and for different plant groups outline the community-level ecophysiological responses to changes in rainfall. While direct measurements of water flux, particularly in roots and stems, are needed, our results provide valuable insights on tropical cloud forest hydrology under scenarios of decreased fog immersion due to climatic changes.

Constraining seasonal and spatial ambient and urban groundwater contributions to streamflow across a mixed land-use regional-scale Precambrian Shield watershed

Groundwater-surface water (GW-SW) interactions are complex phenomena that vary naturally over space and time and are being influenced by environmental change. The Whitson River watershed is a mixed land-use Precambrian shield watershed located in Northeastern Ontario, Canada in which groundwater is a source of municipal water supply and in which groundwater and surface waters are at risk of potential impacts from urban runoff, ongoing municipal drainage projects, periodic flooding, and climate change. This study used watershed-scale synoptic surveys of stable isotopes (δ18O and δ2H) and geochemistry, and corresponding mixing-model approaches (two-component and three-component) to quantify the seasonal and spatial variation in surface water, ambient, and urban groundwater contributions to streamflow. Multiple mixing models were generated based on isotope and geochemical source water identification, and the performance of these models was compared. Mixing-model analyses showed that groundwater contributes a critical, sustaining source to streamflow (> 50 % or more) during summer baseflow conditions, dropping to ∼ 15 % in fall when connection to shield lakes and wetlands dominate. Three-component mixing models showed similar results to the two-component models, refining groundwater contributions into ambient and urban groundwater sources. Estimated urban groundwater contributed 30 % or more to summer baseflow, dropping to ∼ 4 % in the fall. Baseflow estimates derived from graphical hydrograph separation were similar to mixing model groundwater estimates in the summer but suggest this approach overestimates groundwater contributions during the fall. These results demonstrate the complexity of source water contributions to streamflow and the challenges in their determination in mixed-land-use Precambrian Shield landscapes where communities are largely located. Assessment of source water contributions to streamflow across the Whitson River sub-watershed has generated a region-specific conceptualization (e.g. urban versus ambient groundwater) of a basin that is experiencing increased urban development, providing information that will be of value for long term management.

Seasonal and spatial variations of water recharging in the Yangtze River using hydrogen and oxygen stable isotopes

Water and material cycles in rivers are controlled by diverse sources of recharge and flow paths, which exhibit spatial and temporal variations in the contributions of water sources and hydrologic processes. To assess the variation of water recharging, the stable isotope abundances of hydrogen and oxygen (δ2H and δ18O) of 152 water samples collected from the Yangtze River mainstream during May (the flat season) and September (the wet season) in 2021 were analyzed. Bayesian modelling was used to calculate the contribution rates of precipitation, glacier snow meltwater, and groundwater. The isotopic compositions of precipitation and the river exhibited comparable seasonal and spatial characteristics. The Bayesian model results showed that the mainstream was governed by precipitation, with a greater contribution of precipitation in the lower reaches during the wet season. Lakes had a larger contribution during the flat season, as evidenced by the greater increase in the magnitude of δ18O values in the mid-lower reaches during this period. The mid-lower reaches of the river had a decreased river evaporation line (REL) slope, which could be owe to lake replenishment. In addition to intensifying the seasonal variations in the contribution ratios of the lakes, the emplacement of the Three Gorges Dam (TGD) reduced the groundwater contribution of the reservoir. This study enhances our understanding of the hydrological and material cycles in the Yangtze River Basin and provides vital baseline knowledge on the contribution of different recharge sources in the mainstream.

Seasonal transpiration dynamics and water use strategy of a farmland shelterbelt in Gurbantunggut Desert oasis, northwestern China

Farmland shelterbelts provide an ecological barrier to oases, but their growth is inhibited or even dies under water scarcity. Therefore, it is necessary to understand the response of farmland shelterbelts to environmental changes for their own survival in order to promote the long-term healthy development of agroforestry systems and improve water management in oases in the northwest arid region. In this study, we measured the sap flow and environmental factors to determine the transpiration dynamics and its influencing factors. The seasonal variations in water use strategy of Populus alba var. pyramidalis Bunge were identified by using stable isotopes of δ18O in xylem, soil water and groundwater coupled with the Iso-Source model. The results showed that the transpiration of the populus was significantly higher in the growing season (more than 80% of the total transpiration) than in the non-growing season, and the transpiration was closely related to air temperature, vapor pressure deficit, soil water content, and soil temperature. The water use strategy had seasonal variations. The populus obtained water predominantly from 0–40 cm soil water (approximately 75%) in the wet spring and then switched to deeper water sources (40–150 cm soil water and groundwater) as the season progressed. The contribution of deeper water sources increased to 84–92% in summer and autumn. This suggested that Populus alba var. pyramidalis Bunge has ecological plasticity, as it could explore deeper water sources as the water stress increased. The ability to switch rapidly among different water sources could put a plant at an advantage if competition for water occurs within the ecosystem. Our findings can provide insights into temporal transpiration dynamics as well as the strategy adopted by farmland shelterbelts to counteract the drought stress associated with the shallow soils in desert oasis ecosystems.

Toward a common methodological framework for the sampling, extraction, and isotopic analysis of water in the Critical Zone to study vegetation water use

AbstractThe analysis of the stable isotopic composition of hydrogen and oxygen in water samples from soils and plants can help to identify sources of vegetation water uptake. This approach requires that the heterogeneous nature of plant and soil matrices is carefully accounted for during experimental design, sample collection, water extraction and analyses. The comparability and shortcomings of the different methods for extracting water and analyzing isotopic composition have been discussed in specialized literature. Yet, despite insightful comparisons of extraction methods and benchmarking methodologies of laboratories worldwide, the community still lacks a roadmap to guide sample collection, extraction, and isotopic analyses, and many practical issues for potential users remain unresolved: for example, which (soil or plant) water pool(s) does the extracted water represent? These constitute a hurdle for the implementation of the approach by newcomers. Here, we summarize discussions led in the framework of the COST Action WATSON (“WATer isotopeS in the critical zONe: from groundwater recharge to plant transpiration”—CA19120). We provide guidelines for (1) sampling soil and plant material for isotopic analysis, (2) methods for laboratory or in situ water extraction, and (3) measurements of isotopic composition. We highlight the importance of considering the process chain as a whole, from experimental design to isotopic analysis to minimize biased estimates of the relative contribution of different water sources to plant water uptake. We conclude by acknowledging some of the limitations of this methodology and advice on the collection of key environmental parameters prior to sample collection for isotopic analyses.This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water and Environmental Change Science of Water > Water Extremes

Seasonal water sources and response to precipitation events of Calligonum mongolicum at the oasis margin in the Hexi River Corridor

AbstractCalligonum mongolicum is often planted as a windbreak and for sand stabilization on mobile and semi‐mobile sand dunes in extremely arid regions. However, water availability remains a key limiting factor for its survival and population expansion, and water use strategies and responses to precipitation events of this species are unknown. Here, we determined water use strategy of C. mongolicum under extreme arid conditions by measuring the oxygen stable isotopes (δD and δ18O) in xylem water and in potential water sources (precipitation, soil water, and groundwater). We used the IsoSource model to determine the relative contributions of different water sources to water utilization by C. mongolicum. Our results showed that: (1) water sources used by C. mongolicum exhibited seasonal variability, with shallow soil water accounting for 42% of utilization during early spring (April), and deep soil water and groundwater being predominantly used during the summer and autumn and accounting for 61%–84% of utilization, (2) C. mongolicum did not respond to small precipitation events, but responded significantly to large precipitation events. C. mongolicum maintained the utilization of soil water in all layers at 74%–81% of deep soil water and groundwater before a 5.8 mm precipitation event. A precipitation event of 18.8 mm increased the contribution of surface water from 4% before to 17% after precipitation, indicating that C. mongolicum has a strong capacity for self‐regulation and adaptation; namely, C. mongolicum is capable of developing an optimal phenotype through self‐regulation, thereby maximizing water acquisition.

Soil water sources and their implications for vegetation restoration in the Three-Rivers Headwater Region during different ablation periods

Abstract. Amid global warming, the timely supplementation of soil water is crucial for the effective restoration and protection of the ecosystem. It is therefore of great importance to understand the temporal and spatial variations of soil water sources. The research collected 2451 samples of soil water, precipitation, river water, ground ice, supra-permafrost water, and glacier snow meltwater in June, August, and September 2020. The goal was to quantify the contribution of various water sources to soil water in the Three-Rivers Headwater Region (China) during different ablation periods. The findings revealed that precipitation, ground ice, and snow meltwater constituted approximately 72 %, 20 %, and 8 % of soil water during the early ablation period. The snow is fully liquefied during the latter part of the ablation period, with precipitation contributing approximately 90 % and 94 % of soil water, respectively. These recharges also varied markedly with altitude and vegetation type. The study identified several influencing factors on soil water sources, including temperature, precipitation, vegetation, evapotranspiration, and the freeze–thaw cycle. However, soil water loss will further exacerbate vegetation degradation and pose a significant threat to the ecological security of the “Chinese Water Tower”. It emphasizes the importance of monitoring soil water, addressing vegetation degradation related to soil water loss, and determining reasonable soil and water conservation and vegetation restoration models.

Habitat-specific patterns of bacterial communities in a glacier-fed lake on the Tibetan Plateau.

Different types of inlet water are expected to affect microbial communities of lake ecosystems due to changing environmental conditions and the dispersal of species. However, knowledge of the effects of changes in environmental conditions and export of microbial assemblages on lake ecosystems is limited, especially for glacier-fed lakes. Here, we collected water samples from the surface water of a glacier-fed lake and its two fed streams on the Tibetan Plateau to investigate the importance of glacial and non-glacial streams as sources of diversity for lake bacterial communities. Results showed that the glacial stream was an important source of microorganisms in the studied lake, contributing 45.53% to the total bacterial community in the lake water, while only 19.14% of bacterial community in the lake water was seeded by the non-glacial stream. Bacterial communities were significantly different between the glacier-fed lake and its two fed streams. pH, conductivity, total dissolved solids, water temperature and total nitrogen had a significant effect on bacterial spatial turnover, and together explained 36.2% of the variation of bacterial distribution among habitats. Moreover, bacterial co-occurrence associations tended to be stronger in the lake water than in stream habitats. Collectively, this study may provide an important reference for assessing the contributions of different inlet water sources to glacier-fed lakes.

Larger water use efficiency associated with greater dependence on deep water sources in hot-dry valleys with reservoirs

Identifying the carbon–water relationship of plants helps to understand their adaptive water use strategies. The relationship between WUE and the water source remains uncertain in the hot-dry valleys with reservoirs. The leaf δ13C and soil and xylem water isotopes (δ2H and δ18O) were determined to identify the WUE and water source contributions, respectively, in Leucaena leucocephala (Lam.) de Wit communities. We propose a source contributing score (SCS), calculated as a value for the contribution of water from different soil layers (a higher SCS value indicates plants use deeper water sources). The positive relationship between leaf δ13C and SCS (R2 = 0.16, P = 0.022) and the negative relationship between leaf δ13C and topsoil contribution (R2 = 0.21, P = 0.009) confirmed the close association of larger WUE with less reliance on shallow soil water. The redundancy analysis suggested a stronger connection between leaf δ13C and d-excess than leaf δ13C and topsoil moisture content, which emphasized the key role of soil moisture d-excess. Variation partitioning analysis (VPA) suggested soil properties and microclimate explain more than 89.8 % of the variations in tree water use. VPA also suggested different roles of microclimate and soil properties in explaining tree water use strategies. Findings broadened the understanding of the relationship between WUE and water sources and emphasized the key role of soil moisture d-excess in hot-dry valleys with reservoirs.

The effect of shrub cover on conifer water-use patterns, growth and response to precipitation variability in the southern Sierra Nevada.

As wildfires increase in size and severity, large areas of forest are undergoing substantial increases in shrub cover. In forests where water is the limiting resource, the partitioning of soil water between shrubs and young trees may determine how shrubs affect tree growth and water-stress. Here we evaluated juvenile trees (average age=32years) of two dominant conifer species in the southern Sierra Nevada of California (Abies concolor (white fir) and Pinus jeffreyi (Jeffrey pine)) growing in the presence or absence of shrubs. The two shrub species included Arctostaphylos patula and Ceanothus cordulatus, a nitrogen-fixing species. We analyzed the δ2H and δ18O values of xylem water for both tree and shrub species to assess how shrub cover affects the water-uptake patterns of conifers and whether there is niche partitioning between trees and shrubs. We found that growing near shrubs did not have a significant effect on the water source dynamics of either tree species, with similar source water contributions calculated for conifers growing in both the presence and absence of shrubs. Using a tree-ring analysis of growth and δ13C from 2016 to 2021, a period of high precipitation variability, we found that shrub cover had a positive effect on tree growth while decreasing carbon discrimination, which may be due to increased nitrogen availability from Ceanothus cordulatus. Overall, our results suggest that growing in the presence of shrubs does not alter the water uptake patterns of white fir and Jeffrey pine and instead may have a positive effect on the growth rates of these species during both wet and dry years.

A continuation-dynamic constitution analysis approach based on digital stable marker tracing and study on simulation of ecological tidal water diversion

Water Diversion Projects have become increasingly popular in improving water quality in various water ecosystems. However, these projects also require a more comprehensive evaluation. In this study, we introduced a digital stable marker tracing module and proposed a continuation-dynamic constitution analysis approach. We applied this approach to analyze the ecological tidal water diversion in Changshu town, China. The results showed that the mean diversion water age of the Yangtze River water source was 10.80 h, the residence time of the background water source in Baimaotang was approximately 4.0 h, and the contribution of inflow water sources from tributaries accounted for 15% of discharges. The results can demonstrate practicality of our approach in quantitatively evaluating water diversion impacts and optimizing cooperative diversion projects. Furthermore, our discussion led to the design of an ecological tidal water diversion based on optimized cooperative diversion, which showed element-complementary and whole-comprehensive effects. This indicates that the ecological tidal water diversion can extend the impact of cooperative diversion. The continuation-dynamic constitution analysis approach enhances the tracing capacity of inflow constitution and enables the distinction of different time-varying distributions of each inflow constitution. Therefore, this approach holds promise as an embedded “Digital stable marker tracing” module in the model.

Optimization of water-energy-food nexus via an integrated system of solar-assisted desalination and farming

This paper introduces a systematic framework for water-energy-food (WEF) nexus with focus on integrating water desalination (via reverse osmosis and thermal desalination), energy generation (from fossil-based power plants and solar panels), and crop production. Specifically, the paper provides generally applicable and new contributions in formulating WEF nexus problems as multi-objective, multi-period optimization problems with data-driven models based on field work. The paper also established a systematic method for integrating and reconciling farming methods, water technologies, energy-resource selection and operation, carbon footprint, and economic factors. A superstructure representation is used to embed the candidate options and configurations. An optimization formulation is developed to determine the optimal system configuration, water and energy uses and sources, and crop mix selection. A multi-period model is developed to account for the seasonal variability. The optimization model is solved under different carbon-footprint cuts to establish a tradeoff curve between the economic and environmental objectives. To generate the necessary experimental data for a meaningful case study, a year-long field study was carried out to generate experimental data for three fields were constructed in Kuwait using open-field, agrivoltaic, and greenhouse farming methods. The field data were extracted and coupled with the optimization formulation to apply the proposed approach to a case study. First, the optimization formulation was solved to maximize the net profit with no limits on the carbon footprint. The solution of this relaxed formulation gives a maximum profit of 2.127 MM USD/y and an annual emission of 2242 tonne CO2eq. Next, the optimization formulation was solved with the objective of minimizing the total annual emissions. The result was a minimum annual emission of 363 tonne CO2eq that corresponded to 1.366 MM USD/y of profit. The ɛ-constraint method was employed to establish tradeoffs between the economic and environmental objectives. The solutions also provided valuable information on the percentage contribution of solar energy and water sources.

A novel tool for tracing water sources of streamflow in a mixed land-use catchment

Tracing water sources of streamflow in a mixed land-use catchment is critical for predicting pollutant emissions from various human activities to streams but remains a major challenge. A rain event based field monitoring study was conducted in the Jieliu catchment located in the hilly area of central Sichuan Province, southwest China. The ratio of the maximum fluorescence intensities (Fmax) of the two humic-like dissolved organic matter (DOM) components at excitation/emission wavelengths of 255 (315)/415 nm (component 1; C1) and 260 (375)/480 nm (component 2; C2) was proposed as a tracer for quantifying streamflow water sources. Satisfactory performance of using the Fmax(C1)/Fmax(C2) ratio in hydrograph separation of streamflow at the outlet of a forest sub-catchment was verified by through comparison with the hydrograph separation results based on δ18O data. The Fmax(C1)/Fmax(C2) ratio was then applied to estimate the contributions of rainwater and pre-event water sources under different land use types to the streamflow in an agro-forest sub-catchment and the entire catchment. The hydrograph separation results using the Fmax(C1)/Fmax(C2) ratio can be used to support the optimization of water resource management and the quantification of pollutant loadings from major water sources to streams at the catchment scale.

Drought impacts on river water temperature: A process‐based understanding from temperate climates

AbstractHigh river water temperature (Tw) extremes have been widely reported during drought conditions as extreme low‐flows often coincide with high atmospheric energy inputs. This has significant implications for freshwater ecosystem health and sustainable river management practices globally. However, the extent to which different meteorological and hydrological processes interact during droughts to govern Tw dynamics, and how this varies between environmental contexts, remains poorly understood. Here, we review the mechanisms controlling Tw dynamics during droughts across temperate, maritime environments, using the United Kingdom as a detailed case study. We evidence that Tw spikes have widely occurred during extreme low‐flow events observed within droughts, but such trends have been inconsistent due to varying hydroclimatic conditions and river basin controls. To better understand this, we re‐conceptualize the mechanisms governing drought‐induced Tw dynamics operating across three ‘process sets’: (i) ‘energy flux dynamics’ as non‐advective controls on Tw; (ii) the role of ‘reach‐scale habitat conditions’ in mediating non‐advective controls on Tw, including hydraulic properties (e.g., residence time) and physical conditions (e.g., riparian vegetation coverages, wetted perimeters); (iii) ‘water source contributions’ (surface water and groundwater) as advective heat and water flow controls. We review natural and anthropogenic influences affecting Tw controls within each process set and discuss how such mechanisms are likely to change under drought conditions. More systematic research (spanning various river environments and drought severities) is required to test such concepts, with existing scientific knowledge on drought‐induced Tw dynamics being largely gleaned from studies examining non‐extreme low‐flow conditions or with broader focuses (e.g., annual thermal dynamics). We conclude by highlighting critical future research questions that need to be answered to better model Tw dynamics during future droughts and for unmonitored sites. Such scientific advances would more effectively inform how high Tw extremes could be better managed through evidence‐based mitigation and adaptation strategies.

Streamflow Composition and Water “Imbalance” in the Northern Himalayas

AbstractThe Yarlung Zangbo River (YZR) is the largest river in the northern Himalayas, providing crucial water resources for downstream. A full understanding of the streamflow dynamics and regional water budget is critical to secure water security of the Himalayan water tower. Here we establish a comprehensive hydrological model to simulate the precipitation‐runoff‐evapotranspiration‐groundwater‐streamflow complex in the YZR basin. We decipher contributions of different water sources (e.g., precipitation, meltwater, groundwater) to YZR's streamflow and estimate that groundwater sustains ∼36% of annual streamflow in the YZR, while precipitation and melt surface runoff contribute 40% and 24%, respectively. Combining modeling, observation and reanalysis data, our results reveal a water “imbalance” that ∼31% of annual precipitation and meltwater (∼333 mm yr−1 or ∼85 km3 yr−1) is unaccounted for in the YZR basin. We propose that the “excess water” discharges to deep fractured bedrock aquifers, which is promoted by widespread permeable active structures (e.g., faults, fractures). This hypothesis is supported by groundwater storage (GWS) estimates where inclusion of the deep groundwater bridges the discrepancy between baseflow‐derived (shallow) GWS and those derived from the Gravity Recovery and Climate Experiment satellite data. The deep groundwater most likely flows across basins, bypasses streams, and finally discharges to downstream aquifers in the Indo‐Gangetic Plain as mountain block recharge. This study not only provides a comprehensive analysis of the streamflow composition in the YZR, but also contributes to shaping a more complete picture of the functionality of the Himalayan water tower, highlighting the importance of groundwater in regional water transfers.

Isotopic and chemical signatures of high mountain rivers in catchments with contrasting glacier and rock glacier cover

Glaciers and rock glaciers are key elements of mountain hydrological systems, but their relative influence on the chemical and isotopic conditions of streams within the river continuum is still overlooked. During three consecutive years (2019–2021), we studied 24 stream sections in two catchments (Plima and Schnals, Eastern Italian Alps) with varying cover of glaciers and rock glaciers. End-member mixing models based on δ2H and d-excess revealed a large spatial and temporal variability in the contribution of different water sources to stream runoff. Overall, snowmelt (77 ± 17 %) and rainwater (5 ± 5 %) were the largest and the smallest runoff components, respectively. The ice melt contribution was high in streams fed by glaciers (23 ± 15 %) and rock glaciers (16 ± 16 %). In the highly-glacierised Plima basin, the tracer-based estimation of annual ice melt fraction matched reasonably well (90–167%) the mean annual glacial ice loss estimated by geodetic mass balance. In contrast, we found a large overestimation of the ice melt component derived from mixing models in the poorly glacierised (but rock glacier-rich) Schnals catchment. In streams influenced by rock glaciers, at both catchments the particular temporal patterns of electrical conductivity resulted in unreliable estimates of the meltwater/groundwater fractions of runoff. Depending on the local lithology, concentrations of trace elements (Sr, Ni, Ba, Mn, Zn, Al) were high in streams fed by rock glaciers and glaciers, and close/below the limits of quantification in non-glacial streams. In alpine areas, the abundance of rock glaciers can confound the isotopic and chemical signature imparted by glaciers, thus hindering the use of tracer-based methods for hydrograph separation. Under the combined influence from glaciers and rock glaciers, concentrations of trace elements can surpass the limits for drinking water quality even in downstream areas, as we observed at the Schnals catchment for nickel.

Improving the representation of stream water sources in surrogate nutrient models with water isotope data

An important part of meeting nutrient reduction goals in the lower Great Lakes basin and assessing the success of different land management strategies is modeling nutrient losses from agricultural land. This study aimed to improve the representation of water source contributions to streamflow in generalized additive models for predicting nutrient fluxes from three headwater agricultural streams in southern Ontario monitored during the Multi-Watershed Nutrient Study (MWNS). The previous development of these models represented baseflow contributions to streamflow using the baseflow proportion derived using an uncalibrated recursive digital filter. Recursive digital filters are commonly used to partition stream discharge into separate components from slower and faster pathways. In this study, we calibrated the recursive digital filter using stream water source information from stable isotopes of oxygen in water. Across sites, optimization of the filter parameters reduced bias in baseflow estimates by as much as 68 %. In most cases, calibrating the filter also improved agreement between filter-derived baseflow and baseflow calculated from isotope and streamflow data: the average Kling-Gupta Efficiencies using default and calibrated parameters were 0.44 and 0.82, respectively. When incorporated into the generalized additive models, the revised baseflow proportion predictor was more often statistically significant, improved model parsimony, and reduced prediction uncertainty. Moreover, this information allowed for a more rigorous interpretation of how different stream water sources influence nutrient losses from the agricultural MWNS watersheds.

Groundwater recharge in typical geomorphic landscapes and different land use types on the loess plateau, China

AbstractLand use significantly affects the rate and amount of groundwater recharge. To understand these patterns, stable isotope analyses (δ2H and δ18O) and hydrochemical methods were employed to study the recharge and evolution of groundwater. MixSIAR Bayesian mixture modelling and statistical regression techniques were utilized to investigate the influence of land‐use type on groundwater recharge and to calculate the contribution of various water sources to different groundwater types. These findings are important for effective management and conservation of groundwater resources. The groundwater in all studied areas displayed a magnesium bicarbonate type with notable cation exchange, and also demonstrated the dissolution of carbonate and weathering of silicate. Results from the Bayesian mixture model indicate that 69.3% of the groundwater in the Loess Plateau region was recharged by precipitation, while 86.9% of the groundwater in the loess hilly‐gully region was recharged from the surface water. Groundwater recharge was more rapid in the loess hilly‐gully region than in the Loess Plateau and was less sensitive to the land use type in the former. Dryland‐moderate coverage grassland was found to be most conducive to groundwater infiltration, whereas monotypic dryland and high‐coverage grassland inhibited infiltration to some degree. To maintain balanced soil erosion control, an increase the area of moderate‐coverage grasslands in the Loess Plateau region is recommended.

Dry season plant water sourcing in contrasting tropical ecosystems of Costa Rica

AbstractTracer‐aided studies to understand plant water uptake sources and dynamics in tropical ecosystems are limited. Here, we report the analysis of dry season source water uptake patterns of five unique ecosystems of Costa Rica across altitudinal (<150–3,400 m asl) and latitudinal (Caribbean and Pacific slopes) gradients: evergreen and seasonal rainforests, cloud forest, Páramo and dry forest. Soil and plant samples were collected during the dry season in 2021. Plant and soil water extractions were conducted using centrifugation. Stem water extracted volume and stem total water content were calculated via gravimetric analysis. Water source contributions were estimated using a Bayesian mixing model. Isotope ratios in soil and stems exhibited a strong meteoric origin. Enrichment trends were only detected in stems and cactus samples within the dry forest ecosystem. Soil profiles revealed nearly uniform isotopic profiles; however, a depletion trend was observed in the Páramo ecosystem below 25 cm. More enriched compositions were reported in cactus samples for extracted water volumes above ~20% (adj. r2 = 0.34, p < 0.01). The most prominent dry season water source in the evergreen rainforest (74.0%), seasonal rainforest (86.4%) and cloud forest (66.0%) corresponded to well‐mixed soil water. In the Páramo ecosystem, recent rainfall produced by trade wind incursions resulted in the most significant water source (61.9%), whereas in the dry forest, mean annual precipitation (38.6%) and baseflow (33.1%) were the dominant sources. The latter highlights the prevalence of distinct water uptake sources between recent cold front rainfall (near‐surface soil storage) to more well‐mixed soil moisture during the dry season, revealing ecohydrological processing previously unknown in this tropical region.